1. Field of the Invention
The present invention relates to water-dilutable resins, suitable after neutralisation as pigment paste resins, obtainable by converting aldehyde or ketone-based hard resins with multi-functional isocyanates and at least one isocyanate-reactive component.
2. Description of the Related Art
Aldehyde or ketone-based hard resins, abbreviated in the industry to aldehyde or ketone resins, have been known for some considerable time. Due to their specific paint properties such as light colour, resistance to saponification and yellowing, compatibility with other paint binders and very good solubility in polar organic solvents, these hard resins are important raw materials for nitro-cellulose and alkyd resin paints. They have also achieved a major practical significance in special areas of application, such as base resins for solvent-containing universal pigment pastes. However, given the demand for environmentally compatible paints, aldehyde and ketone resins have a significant disadvantage for paint manufacturers and users: they are insoluble in water.
Patent literature contains only a few attempts to manufacture stable, aqueous, dispersions based on aldehyde and ketone resins, as an example described in U.S. Pat. No. 4,644,028 (corresponds to DE-A 34 06 474), in which a protective colloid and special co-polymer are also used.
A further method of making these resins water-soluble or water-dispersible is described in co-pending U.S. patent application Ser. No. 09/166,524, whereby the (hydroxyl-group-containing) aldehyde or ketone resins are converted using acid-group-containing polymers under condensation conditions. After (partial) neutralisation of the remaining acid groups, the condensates become water-dilutable. The condensation process however, significantly increases the size of the molecules; this decreases the level of compatibility with other resins. If the paste resins as described in this application are used in stoving paints, a slight to significant yellowing is observed. In the case of pigmented paints, this can lead to colour changes.
It has been known from U.S. Pat. No. 5,962,582 (corresponds to EP-A 0 838 485) to react hydroxy functional aldehyde or ketone resins with polycarboxylic acids, or esters, halides or anhydrides thereof, to make them water-reducible. The compounds thus obtained have freely accessible carboxyl groups which can cause incompatibility with pigments. Another method is described in U.S. Pat. No. 5,919,859 (corresponds to EP-A 0 838 486), where such aldehyde or ketone resins are reacted with hydrophilic isocyanates made by reaction of (polyfunctional)isocyanates with compounds that have, in addition to their hydrophilic or potentially hydrophilic, at least one isocyanate-reactive group which comprises an active hydrogen atom according to the Zerevitinov test. These products, however, have a fixed ratio of hydrophilic groups and (unreacted) isocyanate groups. Moreover, this process requires a two-step reaction. It is desirable, compared with this state of the art, to provide a simple and easily adaptable process which leads to a variety of products with different properties.